The currently available cooling fan mainly includes a stator, a rotor, a circuit board, a blade assembly, and a frame.
The cooling fan has been widely used to remove heat generated by a variety of electronic devices and components, such as central processing units (CPU), servers, power supplies, communication chassis, and telecommunication base stations. The cooling fan is also often used in very severe environments, such as humid, wet, and salt spray environments. Since general cooling fans are not provided with any protective structure against water and salt spray, the stator and bearings inside the fan are subject to corrosion caused by invading water and salt spray. In some worse conditions, the circuit board of the fan is corroded and damaged to thereby shorten the service life of the fan.
Two solutions have been proposed to overcome the above problems. One of the two solutions is vacuum coating, and the other solution is injection molding. By way of vacuum coating, the stator and the circuit board of the fan are entirely coated with a layer of protective film to achieve the effect of water resistance. However, the vacuum coated protective film is a very thin layer of polymeric material, which is subject to breaking when the fan operates in a salt spray environment. This is because any salt crystals accumulated in the fan would abrade and break the polymeric protective film, resulting in invasion of salty water into the fan to cause short circuit and burnout of the electronic components thereof.
According to the injection molding solution, the stator and the circuit board are first assembled to the fan frame to form a subassembly, and then, put the subassembly in a mold and inject a molding material into the mold. After the molding material is hardened, the subassembly is enclosed in the molding material and removed from the mold. The molding material not only encloses the subassembly, but also fills up all internal spaces in between the stator and the circuit board, so as to provide the effect of water resistance. However, since the injection molded material is thick, it would have adverse influence on the heat dissipation of the enclosed electronic components to result in burned-out electronic components and failed fan.
While the above-mentioned vacuum coating and injection molding solutions are used to protect the electronic components, particularly the circuit board, of the cooling fan against corrosion, short circuit and burnout caused by water and salt spray, the effect that can achieved by these solutions is low. Further, the fan motor being enclosed in the injected molding material has obviously reduced heat dissipation performance to dangerously cause raised temperature of the motor.
In brief, the conventional waterproof and salt spray-resistant structures for cooling fan have the following disadvantages: (1) having limited protective effect; (2) causing accumulated heat inside the fan; and (3) reducing the heat dissipation efficiency of the fan.